Fuel cell system for a mobile work machine

Abstract

The invention relates to a fuel cell system (1) for a mobile work machine, in particular an industrial truck, comprising a hydrogen-powered fuel cell device (4) and a cooling system (11) which comprises a fan device (9), wherein the fan device (9) is designed to generate a cooling air flow for the fuel cell device (4). The fuel cell system (1) has an assembly mounting (3) in the form of a metal cast component to which the fuel cell device (4) and the fan device (9) are secured, wherein the assembly mounting is formed between the fuel cell device (4) and the fan device (9) as an air channel of the cooling system (11).

Description

[0001] Description

[0002] Fuel cell system for a mobile work machine

[0003] The invention relates to a fuel cell system for a mobile work machine, in particular an industrial truck, with a hydrogen-operated fuel cell device and with a cooling system comprising a fan device, wherein the fan device is designed to generate a cooling air flow of the fuel cell device.

[0004] In mobile work machines, in particular industrial trucks, with an electric drive system, it is known to use a fuel cell system to supply energy to the electric drive system.

[0005] Known fuel cell systems comprise a hydrogen-powered fuel cell device, to which oxygen or ambient air is supplied at a cathode region and hydrogen is supplied at an anode region. In the fuel cell device, the oxygen from the ambient air is reacted with the hydrogen, generating electrical energy and waste heat. To dissipate this waste heat from the fuel cell device, a cooling system with a fan device is provided, which generates a cooling air flow through the fuel cell device.

[0006] In mobile work machines designed as industrial trucks with an electric drive system, the fuel cell system is provided as a replacement for a traction battery, for example a lead-acid battery or lithium-ion battery, whereby the fuel cell system is installed in a battery compartment of the industrial truck and thus the maximum external dimensions of a housing of the fuel cell system are predetermined by the size of the battery compartment of the industrial truck.

[0007] The installation space of a fuel cell system of this type is very limited due to the many required components. The components of the hydrogen system, such as a hydrogen tank and the fuel cell device, the components of the electric hybrid system, such as a battery, an electronic control system, a power-voltage converter, and / or a contactor, as well as the components of the cooling system, such as an air duct and the fan device, must be accommodated in a fuel cell system housing designed to fit the size of the battery compartment.

[0008] For a generic fuel cell system, it is also required that the weight of the fuel cell system essentially corresponds to the weight of a lead-acid battery with essentially the same external housing dimensions, so that an industrial truck with a fuel cell system installed in a battery compartment has the same stability as an industrial truck with a lead-acid battery installed in a battery compartment. Due to the limited installation space in the fuel cell system housing, which is designed to fit the size of the battery compartment, it is generally not possible to equip the fuel cell system with additional weight plates that waste installation space.

[0009] The present invention is based on the object of providing a fuel cell system for a mobile work machine, in particular an industrial truck, of the type mentioned at the outset, in which the installation space requirements and weight requirements of the fuel cell system can be achieved in a simple manner.

[0010] This object is achieved according to the invention in that the fuel cell system has an aggregate holder designed as a cast metal component, to which the fuel cell device and the fan device are fastened, wherein the aggregate holder is designed as an air duct of the cooling system between the fuel cell device and the fan device.

[0011] By attaching the fuel cell device and the fan device to a unit holder designed as a cast metal component, a compact unit can be formed, which also forms an air duct for the cooling system between the fuel cell device and the fan device. The unit holder designed as a cast metal component thus has several functions. Firstly, the cast metal component forms a unit holder, to which several components of the fuel cell system are attached, including the fuel cell device and the fan device. This eliminates the need for additional holders and allows for space-saving attachment of the components and thus a space-saving design of the fuel cell system.Secondly, the unit holder designed as a cast metal component forms a second function, a cast air duct for the cooling system and thus part of the air duct of the cooling system, so that the cooling system can be designed in a space-saving manner. Furthermore, the unit holder designed as a cast metal component forms a third function, an additional weight for which no additional installation space is required. With the mass of the unit holder designed as a cast metal component, the weight of the fuel cell system can be easily adjusted to the weight of a lead-acid battery with essentially the same external housing dimensions, in order to ensure that an industrial truck with a fuel cell system according to the invention installed in a battery storage space has the same stability as an industrial truck with a lead-acid battery installed in the battery storage space.

[0012] According to an advantageous embodiment of the invention, the fan device is arranged in the cooling air flow downstream of the fuel cell device, and the air duct is designed as an exhaust air duct of the cooling system. The exhaust air of the cooling system, heated by the waste heat of the fuel cell device, flows through the exhaust air duct. By forming the exhaust air duct from the unit holder, which is designed as a cast metal component, a cast exhaust air duct is thus achieved which, due to its material properties and high mass, can easily absorb the waste heat of the fuel cell device, thereby reducing the required fan speed of the fan device.

[0013] According to an alternative embodiment of the invention, the fan device is arranged in the cooling air flow upstream of the fuel cell device and the air duct is designed as a supply air duct of the cooling system.

[0014] According to an advantageous embodiment of the invention, the unit holder is provided with at least one mounting flange, with which the unit holder can be fastened in a housing of the fuel cell system. A mounting flange can be easily formed on the unit holder, which is designed as a cast metal component, allowing the multifunctional unit holder to be easily arranged and fastened in the housing of the fuel cell system.

[0015] According to an advantageous embodiment of the invention, the assembly holder is provided with a first mounting flange designed to support the fuel cell device. A first mounting flange, to which the fuel cell device can be attached, can be easily formed on the assembly holder, which is designed as a cast metal component.

[0016] According to an advantageous embodiment of the invention, the unit holder is provided with a second mounting flange designed to support the fan device. A second mounting flange, to which the fan device can be attached, can be easily formed on the unit holder, which is designed as a cast metal component.

[0017] According to an advantageous embodiment of the invention, one or more of the following components of the fuel cell system are attached to the unit holder:

[0018] • a purge valve of a purge system of the fuel cell system, which is designed to purge the fuel cell device;

[0019] • a sensor designed to measure a hydrogen concentration in the exhaust air flow of the cooling system.

[0020] A fuel cell system with a hydrogen-powered fuel cell device also requires a purge system with a purge valve that regularly purges the anode area of ​​the fuel cell device to remove unwanted foreign gas components and / or water that negatively impact the performance and service life of the fuel cell device. The purge valve of the purge system can be easily attached to the unit holder, which is designed as a cast metal component, eliminating the need for a separate holder for the purge valve.

[0021] A fuel cell system with a hydrogen-powered fuel cell device also requires a sensor that measures the hydrogen concentration in the cooling system's exhaust air stream. This allows the fuel cell system to be shut down if the hydrogen concentration in the exhaust air stream becomes too high. The sensor can be easily attached to the unit mount, which is designed as a cast metal component, eliminating the need for a separate mount.

[0022] According to an advantageous embodiment of the invention, the unit holder is provided with a third mounting flange designed to hold the flushing valve. A third mounting flange, to which the flushing valve can be attached, can be easily formed on the unit holder, which is designed as a cast metal component.

[0023] According to an advantageous embodiment of the invention, a connecting channel is formed in the assembly holder, connecting the exhaust air duct to the outlet side of the purge valve of the purge system. When purging the fuel cell device, the purge system generates purge gas containing hydrogen. During operation of the fuel cell system, hydrogen is thus released with the purge gas. In order to reduce the hydrogen concentration to permissible values, it is necessary to mix the purge gas with another air stream, thereby diluting the hydrogen concentration. The connecting channel formed in the assembly holder, which connects the outlet side of the purge valve of the purge system to the exhaust air duct, allows the hydrogen-containing purge gas to be easily introduced into the exhaust air duct.In the exhaust air duct, the hydrogen contained in the purge gas mixes with the cooling air flowing in the exhaust air duct, making it easy to dilute the hydrogen concentration to non-critical levels. The unit holder, constructed as a cast metal component, thus has the additional function of venting hydrogen during a purge process of the fuel cell device performed with the purge system. The hydrogen-containing purge gas is released from the connecting duct formed in the unit holder into the exhaust air duct formed by the unit holder and is diluted by the fan device to a non-critical mixture.

[0024] According to an advantageous embodiment of the invention, the assembly holder is provided with a fourth mounting flange designed to hold the sensor. A fourth mounting flange, to which the sensor can be attached, can be easily formed on the assembly holder, which is designed as a cast metal component.

[0025] According to an advantageous embodiment of the invention, the assembly holder has a tunnel-like air outlet, and the fourth mounting flange is formed on the tunnel-like air outlet. The tunnel-like air outlet is preferably arranged downstream of the fan device in the flow direction of the cooling air flow, so that the hydrogen concentration of the cooling air flow discharged into the environment is measured by the sensor arranged on the tunnel-like air outlet.

[0026] According to an advantageous embodiment of the invention, the unit holder between the fuel cell device and the fan device is designed as a buffer storage chamber of the purging system, wherein the buffer storage chamber is connected to the exhaust air duct of the cooling system by means of a throttle connection, and the connecting duct opens into the buffer storage chamber. The unit holder, designed as a cast metal component, thus further functions as a buffer storage chamber of the purging system, into which the hydrogen-containing purge gas is introduced during a purging process of the fuel cell device.By connecting the buffer storage chamber by means of a throttle connection to the exhaust air duct of the cooling system, through which the cooling air flow generated by the fan device flows, it can be achieved with little construction effort that during a purging process of the fuel cell device, the hydrogen-containing purge gas can be introduced into the buffer storage chamber in a short period of time and can be stored in the buffer storage chamber and can be introduced and mixed into the exhaust air duct of the cooling system and thus into the cooling air flow generated by the fan by means of the throttle connection over a longer period of time, whereby the required dilution of the hydrogen concentration can be ensured in a simple manner.

[0027] According to an advantageous embodiment of the invention, the exhaust air duct of the cooling system and the buffer storage chamber of the flushing system are formed by a housing interior of the unit holder, and a partition plate is provided in the housing interior, which is attached to the unit holder and separates the exhaust air duct of the cooling system from the buffer storage chamber of the flushing system. With such a partition plate attached to the unit holder, the housing interior of the unit holder can be easily divided into the exhaust air duct of the cooling system and the buffer storage chamber of the flushing system, which is separated from the exhaust air duct.

[0028] According to an advantageous embodiment of the invention, the partition plate is provided with a throttle connection. This allows the throttle connection between the buffer storage chamber and the exhaust air duct to be easily established in the partition plate.

[0029] According to an advantageous embodiment of the invention, the throttle connection is formed by at least one throttle bore in the separating plate. One or more throttle bores can be produced in the separating plate in a simple manner and with minimal construction effort.

[0030] According to an advantageous embodiment of the invention, the partition plate provides several throttle holes spaced apart from one another in the flow direction of the exhaust air duct. With several throttle holes in the partition plate spaced apart from one another in the flow direction of the exhaust air duct, the hydrogen-containing purge gas can be fed into the cooling air stream at several spatially separated locations in the exhaust air duct, thus ensuring good mixing and high dilution of the hydrogen concentration even with a short exhaust air duct.

[0031] According to an advantageous embodiment of the invention, the aggregate holder consists of grey cast iron or spheroidal cast iron or cast steel.

[0032] According to an advantageous embodiment of the invention, the mass of the assembly holder is configured such that the weight of the fuel cell system substantially corresponds to the weight of a lead-acid battery with substantially identical external housing dimensions. The assembly holder, designed as a cast metal component, can be easily configured and designed to function as an additional weight such that the fuel cell system—optionally using one or more additional weights—has the same target weight as a lead-acid battery of the same size with the same housing dimensions, in order to ensure the stability of the industrial truck when the fuel cell system according to the invention is used in a battery compartment of an industrial truck.

[0033] The invention further relates to a mobile work machine, in particular an industrial truck, having an electric drive system and a fuel cell system according to the invention, wherein the fuel cell system is designed to supply the electric drive system of the work machine with electrical energy, and wherein the fuel cell system has a housing which is designed to be inserted into a battery receiving space of the work machine.

[0034] In such work machines, the fuel cell system can be installed in the battery compartment of the work machine instead of a traction battery, for example, a lead-acid battery. Due to the limited space and dimensions of the battery compartment, the space available for the fuel cell system intended as a replacement for a traction battery is also limited.With the unit holder according to the invention designed as a metal cast component, all components of the fuel cell system intended as a replacement for a traction battery can be arranged in a simple manner in the limited available installation space of the battery receiving space and, due to the high mass of the metal cast component, the fuel cell system can be provided with a target weight that corresponds to the weight of a traction battery that can be inserted into the battery receiving space, for example a lead-acid battery, in order to ensure the stability of the mobile work machine with the fuel cell system arranged in the battery receiving space.

[0035] The invention has a number of advantages.

[0036] With the unit holder designed as a cast metal component, a space-saving and compact arrangement of the fuel cell device, the fan device and an air filter, if attached to the fuel cell device, can be achieved, which makes it possible to form a fuel cell system with a high power density in the installation space specified by the battery accommodation space of a mobile work machine, for example an industrial truck.

[0037] In addition, additional components of the fuel cell system, such as a purge valve and / or one or more sensors, can be easily arranged and fastened to the unit holder, which is designed as a cast metal component, so that no separate holders are required for fastening these components, which would increase costs and require additional installation space.

[0038] The unit mount, constructed as a cast metal component, also forms a cast air duct, for example, an exhaust duct, for the fuel cell system's cooling system. The design freedom of the cast metal component allows for a flow-optimized shape of the air duct to be easily achieved, resulting in low flow losses and thus reducing the speed of the fan. This also reduces the fuel cell system's noise emissions.

[0039] Due to the high mass of the unit holder and cast air duct, which are designed as a metal cast component, the target weight of the fuel cell system, which corresponds to the weight of a lead-acid battery of the same size, can be easily achieved in order to ensure the stability of the mobile work machine.

[0040] The unit holder, which is designed as a cast metal component, also makes it possible to form a large-volume exhaust air duct into which the hydrogen-containing purge gas can be introduced into the exhaust air duct during a purge process of the fuel cell system carried out with the purge system, where it can be mixed and diluted with the cooling air flow in such a way that a critical hydrogen concentration outside the fuel cell system is avoided.

[0041] Further advantages and details of the invention will be explained in more detail with reference to the exemplary embodiment shown in the schematic figures. Figure 1 shows a perspective view of the fuel cell system according to the invention,

[0042] Figure 2 shows an aggregate holder of the fuel cell system according to the invention with the fuel cell device and fan device mounted thereon,

[0043] Figure 3 shows a section through Figure 1 in the area of ​​the aggregate holder,

[0044] Figure 4 shows a section of Figure 3 in an enlarged view,

[0045] Figure 5 shows the aggregate holder in a perspective view and

[0046] Figure 6 shows the aggregate holder of Figure 5 in a top view.

[0047] Figure 1 shows a fuel cell system 1 according to the invention for a mobile work machine, in particular an industrial truck, with an electric drive system that can be used as a replacement for a traction battery in a battery receiving space of the work machine.

[0048] The fuel cell system 1 has a rectangular housing 2 within which the components of the fuel cell system 1 are installed.

[0049] In the upper corner area of ​​the housing 1, which is located at the front in Figure 1, there is arranged an aggregate holder 3, which is shown in more detail in Figure 2.

[0050] A hydrogen-powered fuel cell device 4 is attached to the assembly holder 3. For this purpose, a first fastening flange 5 is formed on the top side of the assembly holder 3—as can be seen in conjunction with Figures 3 to 6—to which the fuel cell device 4 is attached. The fuel cell device 4 is preferably designed as a fuel cell stack.

[0051] An air filter 6 can additionally be arranged on the top side of the fuel cell device 4. The unit holder 3 is further provided with a second mounting flange 8 formed by a flange plate, to which a fan device 9 of a cooling system 11 of the fuel cell device 4 is attached. The fan device 9 is preferably designed as an electric fan.

[0052] The unit holder 3 forms an air duct 10, designed as an exhaust air duct, of the cooling system 11 of the fuel cell device 4 between the fuel cell device 4 and the fan device 9.

[0053] The cooling system 11 comprises the fan device 9, which generates a cooling air flow flowing through the fuel cell device 4. The fan device 9 draws cooling air through two cooling air inlets 12a, 12b, which are formed in the upper region on the opposite end faces 2a, 2b of the housing 2 of the fuel cell system 1, into an air supply duct 15 formed below an upper cover 2c of the housing 2. From the air supply duct 15, the drawn-in cooling air flows through the air filter 6 and then the fuel cell device 4. From the fuel cell device 4, the cooling air heated at the fuel cell device 4 reaches the exhaust air duct 10 formed in the unit holder 3 and, after flowing through the fan device 9, is discharged to the environment via an air outlet 16 of the unit holder 3 and ventilation openings 17 in the end face 2a of the housing 2.

[0054] The cooling air flow is illustrated in Figures 3 and 4 with the arrows KL.

[0055] The fan device 9 is arranged in the cooling air flow downstream of the fuel cell device 4.

[0056] On the exhaust air duct 10 formed in the unit holder 3 - viewed in the direction of the cooling air flow - the fuel cell device 4 is arranged on the inlet side and the fan device 9 is arranged on the outlet side.

[0057] The cooling air drawn in by the fan device 9, which flows to the fuel cell device 4, can also be used as process air for a cathode region of the fuel cell device 4. The assembly holder 3 is designed as a one-piece cast metal component. The assembly holder 3 is preferably made of gray cast iron, spheroidal cast iron, or cast steel using a casting process.

[0058] The unit holder 3 has two side walls 3b, 3c, on each of which a mounting flange 40a, 40b formed by a flange plate is formed, with which the unit holder 3 can be fastened in the housing 2 of the fuel cell system 1.

[0059] A purge valve 20 of a purge system 13 of the fuel cell device 4 is also arranged and secured to the unit holder 3, which is designed as a cast metal component. For this purpose, the unit holder 3 is provided with a third mounting flange 45, to which the purge valve 20 is mounted and secured.

[0060] The purge system 13 of the fuel cell device 4 is designed to purge the fuel cell device 4 at an anode region to which hydrogen is supplied. For this purpose, the purge system 13 comprises the purge valve 20 arranged on the assembly holder 3, which is connected to the fuel cell device 4 via a purge line 21.

[0061] A connecting channel 22 is formed in the unit holder 3, which is designed as a cast metal component, to which the purge valve 20 is connected and which communicates with the exhaust air channel 10. The hydrogen outlet of the purge system 13 is thus integrated into the unit holder 3, which is designed as a cast metal component, via the connecting channel 22.

[0062] The unit holder 3 is further designed as a buffer storage chamber 12 of the purging system 13 of the fuel cell device 4 between the fuel cell device 4 and the fan device 9.

[0063] The connecting channel 22 opens into the buffer storage chamber 12.

[0064] The exhaust air duct 10 of the cooling system 11 and the buffer storage chamber 12 of the purging system 13 are formed by a housing interior 3a of the unit holder 3. The housing interior 3a is bounded by the left side wall 3b, the right side wall 3c, and an inclined or curved bottom wall 3d of the unit holder 3.

[0065] In the housing interior 3a, a partition plate 30 is provided, which is fastened to the unit holder 3 and separates the housing interior 3a of the unit holder 3 into the exhaust air duct 10 of the cooling system 11 and the buffer storage chamber 12 of the flushing system 13.

[0066] As can be seen from Figures 4 to 6, the buffer storage chamber 12 is formed below the partition plate 30 and is formed by the left side wall 3b, the right side wall 3c, and the bottom wall 3d of the unit holder 3, which delimit the housing interior 3a, as well as the partition plate 30. The exhaust air duct 10 is formed by the housing interior 3a between the left side wall 3b and the right side wall 3c of the unit holder 3 above the partition plate 30.

[0067] As can further be seen from Figure 4, the partition plate 30 has a substantially horizontal section 30a, whereby the initial region of the exhaust air duct 10 facing the fuel cell unit 4 has a small height extension in the vertical direction, and a section 30b which is directed obliquely downwards, whereby the end region of the exhaust air duct 10 facing the fan device 9 has an increasing height extension in the vertical direction.

[0068] The buffer storage chamber 12 is connected to the exhaust air duct 10 of the cooling system 11 by means of a throttle connection 35.

[0069] In the illustrated embodiment, the partition plate 30 is provided with the throttle connection 35. The throttle connection 35 is formed by several throttle bores 36a, 36b, 36c, 36d in the partition plate 30, which are spaced apart from one another in the flow direction of the exhaust air duct 10. The throttle bores 36a, 36b are arranged in the initial region of the exhaust air duct 10 facing the fuel cell unit 4, and the throttle bores 36c, 36d are arranged in the end region of the exhaust air duct 10 facing the fan device 9. The cross-sectional area of ​​the inflow opening of the connecting duct 22 is larger than the cross-sectional area of ​​the throttle connection 35.

[0070] The connecting channel 22 with the inflow opening is - as can be seen from Figure 4 - arranged in the vertically lower area of ​​the buffer storage chamber 12.

[0071] Furthermore, a sensor (not shown in detail) is arranged and fastened to the unit holder 3, which is designed as a cast metal component, and which measures the hydrogen concentration in the exhaust air flow of the cooling system 11.

[0072] For this purpose, the assembly holder 3 is provided with a fourth mounting flange 46 to which the sensor can be attached. In the illustrated embodiment, the fourth mounting flange 46 is formed by a mounting surface or a mounting flange formed on the assembly holder 3 on the wall of the tunnel-shaped air outlet 16, so that the sensor measures the hydrogen concentration of the cooling air flow downstream of the fan device 9. The sensor can be mounted, for example, on the mounting surface or the mounting flange by means of fastening screws inserted into receiving bores 47 of the assembly holder 3.

[0073] In the unit holder 3, which is designed as a cast metal component, the exhaust air duct 10 is shaped to ensure optimized cooling air flow with minimal flow losses. This allows the fan device 9 to operate at a low speed.

[0074] During a purging process of the fuel cell device 4, the hydrogen-containing purge gas is introduced into the buffer storage chamber 12 via the connecting channel 22 in the vertically lower region. Due to the cross-sectional area of ​​the throttle connection 35, which is reduced compared to the cross-sectional area of ​​the inflow opening of the connecting channel 22, the purge gas is buffered in the buffer storage chamber 12 and slowly introduced via the throttle connection 35 formed by the throttle bores 36a-36d into the cooling air flow generated by the fan device 9 in the exhaust air duct 10. The exhaust air duct 10 forms a mixing chamber and a dilution zone in which the hydrogen contained in the purge gas is mixed with the cooling air flow, and the hydrogen concentration is diluted such that a non-critical hydrogen concentration is present at the end region of the exhaust air duct 10, where the fan device 9 is arranged.The introduction of the hydrogen at the throttle bores 36a-36d into the exhaust air duct 10 and the mixing and dilution of the hydrogen with the cooling air flow KL in the exhaust air duct 10 is illustrated in Figure 4 with the arrows WL.

[0075] Due to the shape of the partition plate 30 and the arrangement of the throttle bores 36a-36d, even with a short length of the exhaust air duct 10, a good mixing of the hydrogen contained in the purge gas with the cooling air flow can be achieved and a good dilution of the hydrogen contained in the purge gas to a non-critical hydrogen concentration at the inlet of the fan device 9 can be achieved.

[0076] The invention is not limited to the exemplary embodiment illustrated in the figures, in which the fan device 9 is arranged in the cooling air flow downstream of the fuel cell device 4 and the air duct 10 is designed as an exhaust air duct of the cooling system 11. Alternatively, the fan device 9—for example, with the fan rotation direction reversed—can be arranged in the cooling air flow upstream of the fuel cell device 4 and the air duct 10 can be designed as an air supply duct of the cooling system, so that the cooling air flow flows from the fan device 9 through the air duct 10 of the unit holder 3, designed as an air supply duct, then through the fuel cell device 4 and from the fuel cell device 4 via the air duct 15 and the cooling air outlets 12a, 12b. The air filter 6 would then expediently be arranged between the outlet side of the fan device 9 and the fuel cell device 4.

Claims

Patent claims 1. Fuel cell system (1) for a mobile work machine, in particular an industrial truck, with a hydrogen-powered fuel cell device (4) and with a cooling system (11) comprising a fan device (9), wherein the fan device (9) is designed to generate a cooling air flow of the fuel cell device (4), characterized in that the fuel cell system (1) has an aggregate holder (3) designed as a cast metal component, to which the fuel cell device (4) and the fan device (9) are fastened, wherein the aggregate holder is designed as an air duct of the cooling system (11) between the fuel cell device (4) and the fan device (9).

2. Fuel cell system according to claim 1, characterized in that the fan device (9) is arranged in the cooling air flow downstream of the fuel cell device (4) and the air duct (10) is designed as an exhaust air duct of the cooling system (11).

3. Fuel cell system according to claim 1 or 2, characterized in that the unit holder (3) is provided with at least one mounting flange (40a; 40b) with which the unit holder (3) can be fastened in a housing (2) of the fuel cell system (1).

4. Fuel cell system according to one of claims 1 to 3, characterized in that the unit holder (3) is provided with a first fastening flange (5) which is designed to hold the fuel cell device (4).

5. Fuel cell system according to one of claims 1 to 4, characterized in that the unit holder (3) is provided with a second fastening flange (8) which is designed to hold the fan device (9).

6. Fuel cell system according to one of claims 1 to 5, characterized in that one or more of the following components of the fuel cell system (1) are attached to the unit holder (3): • a purge valve (20) of a purge system (13) of the fuel cell system (1), which is designed to purge the fuel cell device (4); • a sensor designed to measure a hydrogen concentration in the exhaust air flow of the cooling system (11).

7. Fuel cell system according to claim 6, characterized in that the unit holder (3) is provided with a third fastening flange (45) which is designed to hold the purge valve (20).

8. Fuel cell system according to claim 6 or 7, characterized in that a connecting channel (22) connecting the exhaust air channel (10) to the outlet side of the flushing valve (20) of the flushing system (13) is formed in the unit holder (3).

9. Fuel cell system according to one of claims 6 to 8, characterized in that the unit holder (3) is provided with a fourth fastening flange (46) which is designed to hold the sensor.

10. Fuel cell system according to claim 9, characterized in that the unit holder (3) has a tunnel-like air outlet (16) and the fourth fastening flange (46) is formed on the tunnel-like air outlet (16).

11. Fuel cell system according to one of claims 8 to 10, characterized in that the unit holder (3) between the fuel cell device (4) and the fan device (9) is designed as a buffer storage chamber (12) of the purging system (13), wherein the buffer storage chamber (12) is connected to the exhaust air duct (10) of the cooling system (11) by means of a throttle connection (35) and the connecting duct (22) opens into the buffer storage chamber (12).

12. Fuel cell system according to claim 11, characterized in that the exhaust air duct (10) of the cooling system (11) and the buffer storage chamber (12) of the Flushing system (13) are formed by a housing interior (3a) of the unit holder (3) and in the housing interior (3a) a separating plate (30) is provided which is fastened to the unit holder (3) and separates the exhaust air duct (10) of the cooling system (11) from the buffer storage chamber (12) of the flushing system (13).

13. Fuel cell system according to claim 12, characterized in that the partition plate (30) is provided with the throttle connection (35).

14. Fuel cell system according to claim 13, characterized in that the throttle connection (35) is formed by at least one throttle bore (36a; 36b; 36c, 36d) in the partition plate (30).

15. Fuel cell system according to claim 14, characterized in that in the partition plate (30) there are several throttle bores (36a; 36b; 36c, 36d) which are spaced from one another in the flow direction of the exhaust air duct (10).

16. Fuel cell system according to one of claims 1 to 15, characterized in that the unit holder (3) consists of grey cast iron or spheroidal cast iron or cast steel.

17. Fuel cell system according to one of claims 1 to 16, characterized in that the mass of the unit holder (3) is designed so that the weight of the fuel cell system (1) substantially corresponds to the weight of a lead-acid battery with substantially the same external housing dimensions.

18. Mobile work machine, in particular industrial truck, with an electric drive system and a fuel cell system (1) according to one of the preceding claims, wherein the fuel cell system (1) is designed to supply the electric drive system of the work machine with electrical energy, and wherein the fuel cell system (1) has a housing (2) which is designed to be inserted into a battery receiving space of the work machine.

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